First of all, I don't get splitting the launcher instead of running 1 single 15-pack. It'll make your timing funny as they have different cycle times. But, whatever, that's up to you. I get that it's a little faster. I just don't see it as significant with so few missiles.
Second, 2 tons of LRM ammo is 24 volleys with 15 tubes. If you're going through more than that with those piddley launchers, you're playing wrong. If you want to have a few LRMs as a chase/closing weapon, that's fine. But if you're standing off in an Atlas trying to play support with only 15 missiles, you're crippling your team. An assault, whatever role they choose, simply needs to be doing more than that, period.
Third, that is a weak loadout for an assault. There's mediums with better weaponry, and they move faster.
If you want a mix of weapons like that, try this
Mixed Role Atlas. I generally find 30 rounds to be plenty for an LB-X, especially if you plan to play any support at all, but I loaded 45, just in case. It's got 36 volleys of 30 LRMs, which I believe is plenty for mixed role, but you could get 6 more by trading a ton of LB-X ammo, and another 6 if you want to move the ammo from LT to RT, so you only need 1 CASE and drop 1/2 ton of armor (to 73 per leg). Artemis and TAG will make your LRMs far more effective, though it gives up 1 ML for close action. With 13 DHS you need very minor heat management at close range, and none at all with your missiles.
If you'd rather play close support with LRMs for closing/chase weapons you could try this
Close/Mid-range Atlas. It's more of a constant-threat build. The heat sinks can pretty much run it all day if you only use the appropriately ranged weapons, or you can make a substantial Alpha when the time is right. You could also drop 1 ton of LB-X ammo for another heat sink. This modified version
Close-range Atlas drops the Large Lasers to Mediums, boosts the engine and increases heat sinks. It's got less firepower overall and less mid-range in particular, but is much more heat-conscious. In both cases, it drops TAG and Artemis IV since the effectiveness increase for so few LRMs doesn't seem worth it.
Personally, I feel that LRMs are only useful in numbers and find anything less than 30 to be a waste of time. For only 1 ranged weapon, I'd go something like this
Close Assault Atlas. With 18 DHS, you can go pretty wild. The Gauss gives you much more threatening reach than 15 LRMs and can be mixed in with your short-range weapons without worrying about heat, and has enough ammo to do both.
If you want to play full-on support, which I don't personally like for this variant, I'd go something like one of these:
Support RS or
Support RS v2.
In all the builds I only used 1 ton of AMS ammo because there's just not that many mechs launching enough missiles that you care about AMS without launching enough to overload it. But you can easily fit an extra ton into any of these builds if you prefer.
DON'T put it in the head. The new override system makes it far too easy to get ammo explosions and it will kill you instantly.
The Front/Rear Torso armors are simply Smurfy's default when you hit "max armor." I generally put quite a bit more to the front than these.