The primary limit early is era credits, and if you've reached node 50 on the Episode Track then you'll be getting TONS of credits over the next week. Use those to upgrade your toons every single day, even in-between runs in the coliseum. Leave a couple runs until after your daily changeover (whenever that is), get more cash from doing dailies, upgrade again, run the coliseum again.
You should be beyond level 15 and it doesn't require L25 to beat the L25 enemies, though you will need to get both of your toons above L20.
If it's worth it to you, you can also spend a few crystals on materials (that's the better investment than cash right now, since cash is easier to get while at the end of the EpTrack).
I don't know how easy it is to do without spending crystals - I never spend $$, but I do spend crystals - but it's definitely doable.
If you want more specific help, just give us more info about your account and we can maybe do more.