I am attempting to make a 15 point buy mesermist and I find I'd greatly prefer his stats if I just went heavy on the charisma and made him a caster. Is it a viable choice? Looking at the spell list and the gaze it feels like I could still contribute well but I am not certain.
This can really depend on your game; if there are tons of enemies with early immunity to mind affecting effects, you're screwed.
If it's a social heavy game; you can be obnoxiously strong.
I'd suggest Human, and with your feats: Deceitful and Cunning Caster. This means you make bluff checks for people to realize if you are casting spells. It's very strong on Psychic classes, especially mentalists, because their spells ignore most of the conditions that impose penalties to your bluff check, within the feat
You can force a -2 to -3 to saves without any real effort (by all rights, in terms of your effective save DC's, you are basically bumping your 6 level class to a straight 9), and you can even force enemies immune to mind affecting spells to fall victim to your list via psychic inception. And that is ignoring how you have a list somewhat similar to bards, meaning you can just buff when all else fails.
There is little reason why you can't be a caster alone.
How many encounters are you likely to get between rests? A low number is better for a 6-level caster trying to rely on spells.
Are there others in your party who could make use of the gaze will save penalty?
Is your party big enough that you might be able to get by just using a whip to trip or disarm sometimes?