In Bloons TD Battles, the default speed is the regular speed. In BTD5 however, I like to speed it up. When playing BTD Battles, I'm not used to the slow speed. Is it possible to speed it up?
No you can't. On the wiki it says:
Fast Forward does not exist in Bloons TD Battles, probably due to the fact that players can lag their opponents with this and win Medallions for free.
And as annoying as it may be to not be able to fast forward if they added it there will always be people who will cheat using this.
Source: BTD Wiki - trivia section