In effect the op is saying I know nothing about sailing but am concerned that it might get too windy and a large motor
might get me home quick before I get into trouble.
By quick he means at over 15 k/hr.
Most monohulls of that size will max out at about 7 k/hr, not always in the direction you want to go. They won't go faster under increased power for the reasons others have given. Fuel
costs would rise exponentially. Further sea state would limit speed to around 7 knots, or the boat would break up.
There are better means of avoiding trouble. Namely choosing area and weather
There are also means of handling adverse weather
namely by reefing, and other ways and threads on handling storms.
The prospect of bad conditions can be scary however part of learning
to sail, is to acquire confidence
in handling this and avoiding
It is those 3 aspects I suggest you focus on, in initially small steps, before you get carried away with plans.