For sure. The tripods weigh nearly as much as the weapons themselves (9ish kilos for a -60 and -240B), plus spare barrel, optics...
A fully kitted out M4 weighs considerably more than the rated 3.5 kilos (loaded), though not 14 kilos. The real issue here is not the weight in the short term. It would be a world of suck to carry around some of the weapons in the BattleTech universe on a regular basis. But it could be (and is today) done, though only by a few in each infantry unit. The trouble is that in the long term, all of the infantrymen are going to be broken down physical wrecks.
Luckily, in the BTU, that isn't a problem. Most infantrymen don't live past their first firefight or two. :(
My wife got that same sniper rifle at the 8th Army NCO Academy back in the '80s! :D
Well, tell her thanks. I appreciated it. By the time it got around to me, it had a distressing tendency to lose its buttstock, and the spring, the bolt...
Did I mention that NTC is a dusty place? Well, it is.
But back on topic, I think that the writers/developers should think more about the weights of the things they make. of course, in a world with fourteen-tonne autocannons and 500-kilo M2HB equivalents...