its a woody shrub so you are best giving it a good prune [down to 6 -12"] now really. It wont split but if you want to take cuttings then a non flowering shot in the summer is your best optin.

We prune ours down to about a foot, but after flowering rather than in Spring. If we do not remove all the spent flower heads then we get hundreds of seedlings all round the bush.

I think the Spireas are very easy about shaving bits/lots off them to get the height and control you want. It is only a short time ago I pruned about 8 inches off one of them before it got too active. It is now a wonderful colour made by tiny shoots. Also a much better shape and height. A bit late to prune now if in active growth. you have all the time between end of flowering and early spring to severely or gently prune.