So I'm using JSDB on the EV3 (which is an ARM5 running Debian Stretch).
For the API, to answer your question, all the load()'s are happening at startup and are very costly getting things going.
The only downside I've had with JSDB is the fact that it is still on ES5 (with a few small gaps, like missing some of Object). I'd love to see a newer version that could run ES6, and maybe even the proposed ES7 that'll come in 2020. Eclipse hooks for debugging would also be a really nice addition, but alas, all of that takes lots of time from experienced people, and my knack is at transcoding APIs, not writing interpreters. So for now, I'll continue using ES5 on JSDB on EV3Dev for Lego and hopefully our team will continue doing well when the compete . I'm just trying to get them onto a platform that is both competitive and non block-programming (like the mindstorms environment).