Pretty much what these guys have said I fully agree with. Tremonti played Rectos for years so that the tone he built into the MT15 near as I can tell. MT15 modern recto tone with it alot of amp for the money and it was designed to be a good amp for beginner and intermediate players according to Tremonti himself.
The SLO, well it's an SLO.
I don't think the grass is much greener on the other side of that good sounding Splawn you have, but changing it up is subjective. I still kind of hear the SLO30 even though it sounds good it's 30 watt stature may leave you disappointed next to a 100 watter with a good master volume live. The smaller iron contributes to less punch and it will not hit like a 100 watter even at comparable volumes.
I usually pull two tubes on my 68 plexi for some volume control and it still hits harder and a more expansive low end and overall dynamic range than my 72 50 watt superlead. They both sound great but the 50 watter feels noticeably more diminutive in the low end and punch department. If you can find an old article about the Mojave Scorpion 50 watt plexi which was the Peacemaker but 50 watts Vic was disappointed because the 50 watt with 50 watt power and output transformer just wasn't delivering the same punch and feel as the 100 watter side by side.
His solution... Run bigger iron. So he used 100 watt transformers and he halved the impedance just like you would pulling two power tubes on a 100 watter then hardwired the speaker jacks accordingly... and the Scorpion now punched like a 100 watter but ran at 50 watts.