A set of this length is a great reference set to use from time to time. Maybe early in the season you can handle the set on a 1:30 per/100 base. With some training, in 3-4 weeks you may try it again one of two ways: bring that down to a 1:25 base per 100 or keep the base at 1:30 per 100, but try to swim at a faster pace than the first time. If you can achieve either of these, then chances are, your swimming fitness has improved.
Along with some longer endurance sets this time of the year, consider one workout every week or two that you devote more time to swimming the other strokes. This will help your feel for the water, provide a great workout using muscles a bit differently and giving your freestyle muscles a little break.
Keep blowing bubbles and have a great week!