E-4 putting 20% into ROTH TSP. Should I open a ROTH IRA and move 15% into that and drop my TSP to 5%?

If it was me, I’d do the Roth IRA over the TSP but only cause I feel like the support is better on the civilian side.

But honestly, it really does not matter. You can’t go wrong either way.

Edit: get the 5% match first then I’d do 15% Roth ira

IRA plans are more flexible with what they offer as you go through life. You’re doing great! As others have said you can’t go wrong either way, but you may find you get more benefits out of having the majority in an IRA.