The person making something slowly may be enjoying the part you want to skip.

Speed assumes the finished object is the point. For some people the middle is the point: the sanding, the second draft, the hours that produce nothing anyone can see. Offering a shortcut there is offering to remove the part they started for, however helpfully it is meant.

Before you suggest a faster method to someone, ask whether they want it done or want to be doing it. If it is the second, admire the work in progress and keep the efficiency to yourself.