Architect1776 wrote:
You have an excellent camera.
Perhaps as a suggestion, rather than waiting to arrive at the destination, that you put the 35mm f/2 DX lens on your D5300 and go to darker lit interiors (Local Catholic church for example) and take non-flash photos. Then you will know ahead of time then if it works for you or not.
All can sit here and pontificate and speculate but only you know what works and is acceptable to you.
So do the simple test, 10 minutes at most and you will know.
Agree! I've shot many cathedrals and a lot of street architecture in Europe - film and digital. It's easy to buy another camera. More work to be objective and conduct conclusive testing with what you have. Doing some interior test shots before the trip is the right idea. The OP may not need to buy a thing. If the 5300 yields satisfactory low light results (for them), then done. If not, look at a used or refurb D7200 or D500. But, with skill and a good lens, the D5300 may be enough. It Still boils down to actual D5300 testing under simulated trip conditions.