So I am trying to make a Class for playing a Witcher like from CDProjekt Red's The Witcher licensed games. I would appreciate any help I can get. So far I have them leveling to 15th with a slow EXP Track. They can do 3 spells at first level. They also have Infravision up to 30 feet. Oh and they get +2 to STR, DEX and CON. Any tips or ideas would very much be appreciated.

Don't know the Witcher game, but giving starting witchers three times as many spells as magic-users sounds completely broken.

And you can't balance that away with a level cap. L15 is so high it might as well not exist, and at best, level caps are only loosely correlated with balance. They're really about enforcing demihuman scarcity and establishing a humanocentric world, anyway; because from a balance perspective giving the weakest demihuman class the lowest limit (halfling makes zero sense. And slowing their XP progression also doesn't work, beyond a certain point. The geometrically increasing XP requirements means everyone stays within a level or so of everyone else, and even if you try to be very punitive (say 16,000 XP to reach 2nd level) that just means means the witcher will end up 3 levels behind the fighter. Which means you have the tricky (impossible) feat of balancing witcher 1 against fighters 1, 2, 3 and 4 (because the witcher won't reach 2nd level until the fighter hits 5th level), while still making sure a witcher 6 and a fighter 9 are comparable. And this just gets worse after name level, because XP requirements flatten out -- unless it's tweaked, the fighter will be gaining a full 8 levels for every 1 level gained by the witcher.

Class balance is really about making sure all classes are both good and bad at different things, and using XP to give a minor perk/hindrance to the ones that are slightly stronger/weaker overall. You can't treat it as a point buy system, and just stack on powers indefinitely. The stat bonuses are also a poor fit, because the game tends to handle classes that should be weaker/stronger with minimums and primes/XP bonuses, not flat bonuses. Instead of +2 to 3 stats, saying a witcher must have a minimum of Str 9, Dex 9, and Con 9 would be more in keeping with how the other classes work. And what about the other core class features, like HD, XP bonuses, armor, weapons, magic items usable, spell list, XP to 2nd level (which gives a reasonable idea of XP through L9 or so), etc.?

I've been toying with a Witcher style class for 1e. Mine is closer to a 2e style ranger as its base (since they are essentially monster hunters and Geralt reminds me more than a little bit of Drizzt), but they start with a small number of random special abilities  (things like infravision and spell use and monk abilities) and gain more randomly as they level.  

Which isn't really true to the PC games, since they use a talent tree system, but I think it maybe more true to the books where Witchers are mutants, basically. And I think it's more fun.

Mine also improve abilities like the 1e Cavalier, where all the physical stats have a d100 in addition to the ability score and every level you roll some d10s to add to that, which can raise up the ability score a point.  

I wouldn't worry about balance, since LL (and B/X) classes are not balanced to begin with.  "Hey, I'm a Halfling! I'm a worse fighter that needs more XP and I don't even have thief abilities for some reason" . "I'm a cleric, I can fight well, wear the best armor, cast a lot of spells and have the easiest XP advancement. Suck it thief!"

But the XP advancement is a thing you do need to watch. Make sure the class is never more than 1-2 levels behind other classes. That's generally the case with AD&D/Greyhawk style multiclassing (and the LL style Elf which is basically juat  Fighter/Magic-User).

So a Monster Hunter, eh?

What you want is Witcher-Sight, as opposed to Infravision. Infravision is also permanent, which Witcher-Sight isn't.

I wouldn't give him spells, but Cantrips. Those should be rather weak and few and far between and not change too much over the span of 15 levels.

Everything else is pretty much a typical Fighting-Man.

I'd say most of the witcher special powers come from potions. The witcher being alchemically transformed so that they don't die when using their special mixtures.

Give the witcher some minor spells at mid level and a potion using ability whereby witcher grade potions will work on them really well and kill anyone else who uses them and non-witcher potions have limited effects on a witcher. Keep track of toxicity so they don't take vast amounts of everything all at once and give them a potion that clears everything else from the system and you should be good to go.

Wow; that sounds like a pretty crazy level of 'grade inflation'. This sort of thing has been part of cannon D+D since 1E Unearthed Arcana, so you're in good company at least. But, I am not aware of an example of a 'super class' that didn't turn out to be a mess in play. A much simpler solution: If you want to play a really tough fighter magic user monster hunter, just write up a high level PC with two or three of the normal established classes. Your campaign will start a bit 'juiced' but the game will still consist of components that are known to work well together after decades of play testing.