That's one of the small leaved Lilacs; note the simple leaves with opposite
arrangement. Spirea members will have alternate
arrangement of simple leaves.
One common form is Syringa patula
'Miss Kim', as I learned it. Apparently, it has been renamed as Syringa pubescens
Manchurian Lilac (Syringa pubescens subsp. patula 'Miss Kim')
Other small leaved species include Syringa meyeri
and Syringa microphylla
. There are doubtless more clones of each of these around.