Of course, you could write 12/8. Then there would be 7 Bars of 12/8 in the first part (until it is repeated).
There may be several possibilities but I would write it like this:
3/812/86/86/8 [or 3/83/8 instead of the 6/8 because the first triplet has also its own bar] 12/812/86/8[which again could be two 3/8]
12/815/8:
