Foot shlogging naked Veterans with Plasma guns? They are as good as dead. If you must leave them on foot, they need Forward Sentries for Camo Cloaks so they can hide in ruins, bushes etc. At this point they are better off with and assortment of Sniper rifles, Auto cannons and/or a Lascannons.
Remember, Plasma guns need to be within 12" to maximize effectiveness. How are you going to get them that close on foot? You can't just expect your enemy to always come walking right up to you. A better Plasma load out is simply:
Vets, 2 Plasma Guns, Chimera - 155
You need to ask yourself, how are you going to capture objectives instead of just passively sitting on your own. You need a plan for this. Consider dropping a Sentinel squad and putting those Vets in a Valkyrie. With those 3 Plasma guns they can drop down from the Valk, rapid fire with Plasma and annihilate a camping enemy troop while stealing the objective. Even better, put a Primaris Psyker with them and roll on the Divination table to possible give the Valk/Vets a 4++ invulnerable or trade in your power for Prescience to twinlink the Veterans.