Welcome to Android Central! Do other apps do the same thing over the Bluetooth speaker, or only Spotify?
Wi-fi can sometimes interfere with Bluetooth if the former is on the 2.4 GHz band, so if your wi-fi is on, try using the 5 GHz band (if available through your router), or try changing the router's 2.4 GHz wi-fi channel (which requires logging into the router settings--see the router manual for instructions).
Other electronic equipment at home can also use the 2.4 GHz band (like older cordless phones). You might try testing the Bluetooth speaker somewhere away from your house to see if the playback is smoother.