Speaking as someone who has their own Catapult C4 and played it alot, I think I might recommend a few skill tree changes. I think the OP should dump the entire right side of the Firepower tree and devote all those skill points into the Survival tree. The reason I say that is because I don't think the right side of the weapons tree is really necessary.
My Catapult C4 carries a pair of LRM-15s too. When using those alone, I have more than enough heat sink capacity to keep up with the heat generated, and only start overheating when I start throwing my SRMs (I have an XL engine in my C4) too. The OP doesn't have SRMs. This means the right side Heat Gen nodes are superfluous; you can get by with just the left side ones.
Likewise, the Range nodes are also not necessary. Oh they're nice to have and you need to get SOME to get the nodes you really want. But at the end of the day, most of your LRMing should be done at far less than 900 meters anyway.
Cooldown nodes are useful. The more you get, the more frequently you can fire your LRMs and the better your DPS. But I find the base refire rate of LRM-15s already to be plenty fast enough for most battlefield purposes. You can do without the right side Cool Down nodes.
So, if you do remove all the right side nodes from the Firepower tree, what do you do with them? Throw them into the Survival Tree. Get every node you can that buffs Armor and Structure points. If you're like me and like to fight from the second line, then anything that increases your mech's survivability - and especially anything that prolongs keeping your arms where your LRM launchers are - increases your ability to dish out damage for longer.
Yeah yeah, I know I said my mech carries an XL engine that doesn't improve survivability. But you know what? 90% of my mech getting killed is due to CT destruction, and XL engines is no help there, so I might as well use an XL. Your experience may be different (because you're better at presenting your sides to return fire than I am), so I'm not recommending that you use an XL too.
Edit: Whoops, checked your loadout again and saw that you ARE using an XL engine.
Edited by evilauthor, 09 June 2017 - 10:47 PM.