As far as I can tell there are no Leves for Mining beyond level 15, if anyone knows of any I'd appreciate the info.

Other than doing the daily provisioning for your grand company (hand in HQ stuff where possible, you can only do it once a day so make the most of it) I have discovered no way to speed up the mining process other than to buy the field manuals from the Grand Company quartermaster.

Lvl 28 Mining currently, I think I might stop trying to level it once I can get Mithril, which should be in 8 levels (I think).