Investigate performance differences in environments.

rems-dev is faster than FD test REMS (about 3x so 100ms vs. 300ms). Could the difference be due to:
- [ ] email being sent for real (to all handlers)
- [x] translations are not using a cache
- [x] one handler email is wrong and gives out an error (https://github.com/CSCfi/rems/commit/f1d1f01cca223cf63d3db01615ceee76efacbfb5)
- [x] many more handlers (10-26)
- [x] larger forms (128 fields) (larger test data generated in #3105)
- [ ] event notification integration
- [ ] many attachments (esp. answer attachment fields)

Production is maybe even slower (for full cache reload at least, seems not for single events).