I have FP Open OS on my phone since it was available.
Yes, in the beginning getting a fix on the location was taking to long.
Now it has improved very much.
On F-Droid you can find MozillaNlpBackend which I have installed together with UnifiedNlp (no GAPPS) and LocalGsmNllpBackend. Perhaps this is a little over the top. but it works for me.
For installing FP Open OS please read the installation instructions at this page.
I can recommend the following wiki first steps on FP Open.