How long would it take you to do the same ride on 17 lb bike? The Creo with SL has a nominal rating of 480 Wh. Let's say 450 Wh is usable. If you would normally take 8 hrs to do 150 miles that would be an avg 18.75 mph. 450 Wh of the Creo would equal 450Wh/8h = 56.25 Wh/h giving an avg assist of 56.25W/18.75mph = 3 Wh per mile. On an SL bike on flat ground with no wind that is quite a bit of assist.
If you take 10 hrs to do 150 miles = 15mph, 45 Wh/h, average assist is still 3 Wh per mile. As Nova Haibike notes whether or not the Creo assist is adequate for you is largely dependent on your power/weight as well as the terrain and wind conditions for your ride.
If you take 6 hrs to do 150 miles you don't need a Creo.