The word speed is used here in the dated sense of “success, luck”, though probably with a pun on the sense “velocity”. Compare the same in Low Germanje gröter Hast, je minder Spood.
Russian: ти́ше е́дешь, да́льше бу́дешь(tíše jédešʹ, dálʹše búdešʹ, literally “the slower you ride, the farther you'll get”), поспеши́шь — люде́й насме́шишь(pospešíšʹ — ljudéj nasméšišʹ, literally “if you do it in a hurry, you’ll make people laugh”)