To be entirely frank, I'm a native speaker, but for the overwhelming majority of my day I only use English, and my Russian has started to wane. My job requires me to cycle through a couple of financial transactions a day and those tend to include the pronounced statements of order numbers and sums of money. I tend to get away with saying order numbers digit by digit, yet sums of money? That gets me very odd looks.
If I take a very long while, like 5 minutes, I can finally conjure up the "в сумме сорока шести тысяч семиста девяносто восьми рублей двух копеек" that is needed, but the delay is as painful and long as to cause issues.
I am seeking advice from people who have learned this language intentionally: What do you do to refresh and keep up with the complex numerals? My head has been overheating because of this. Maybe an exercise or something? I don't have my old Russian language school textbooks to fall back on.