are you new to DaVinci or not? if you have not already done all the simple optimizations in preferences they can help.
may be worth drooping by DaVinci's forums for more specialized advice.
simple things to do is look at activity monitor and get
https://bjango.com/mac/istatmenus/ or
https://sourceforge.net/projects/hwsensors/ one of those apps let you watch system use.
that will show you where your main slow down is & if you have any budget to spend focus there.
edit you gave almost no info on system, if you need more speed the simplest "free" thing to do (if you are are a budget) is if your video files are h264/h265 then convert them to a good proxy format like DNxHD (but im a bit outdated on that so worth double checking)
edit 2
if you have a budget CPU/RAM upgrades will be the cheapest/biggest speed up
DaVinci loves GPU power
look in to maybe some SSD drives (depends on codec rely as a value to speed trade off)
