It is safe and it won't make your eyes worse if you wear fulll power lenses. The reason why your eye doctor offered you -1.50 instead of -2.50,as your power is not that strong, your power can be adjusted by wearing relatively weaker power lenses. This is a way to reduce the difference between in power between the two eyes thus to make your glasses easier to wear and adapt to.
If you wear glasses at full power, then there is a big difference between two eyes. You will find difficult to get used to your glasses. If you wear a weaker prescription glasses, which will narrow the gap between the two eyes, your eyes can work together more easily. Hence you can adapt to your glasses easily. So just choose the one that is comfortable to wear.