Thanks for the question.

In looking at your pictures, two things stand out regarding the leaves:  the holes and for some a yellowing around the holes.  I suspect that your spirea are experiencing Cylindrosporium Leaf Spot.  This is a fungal disease and is spread from one plant to another through spores.  You would not have detected this disease last fall when they were planted.  It would first appear this past spring.  Often but not always this spread is promoted by how you might have watered your spirea.   These spores are found in the ground and if watering is done from above, splashing water will lead to these spores landing on adjoining plants at the beginning of the growing season.  You would see leaf damage first appearing near the base of spirea.  It would be better to water at their bases, preferably by means of soaker hoses.  One of the characteristics of this disease is extensive leaf drop around this time of the year (mid-August).  The following will give your further information about leaf spot and remedial procedures that can be taken:

https://homeguides.sfgate.com/spirea-diseases-68929.html

http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/leafspotdis.html

https://gardening.yardener.com/Problems-Of-Spirea

(at the above site scroll down to where leaf spot is described)

Thankfully spirea do not seem to experience serious damage from this condition.  At this point removal of all affected leaves would be wise to minimize future fungal spread.  Any branches that are dead (scrape the bark away in a small area and if the underlying plant tissue is not green, it is dead).  Place these leaves and branches in a trash bag and dispose of accordingly.  It would appear that you have mulch spread up to very near the bases of the spirea.  If so, this will cause a retention of moisture and spores under the shrubs.  This will lead to a spread of the disease.  Keep an area clear of mulch within about 12 inches of the bases of the spirea.

Leaf spot can also have a bacterial cause.  Treatment and prevention of this is very similar to what are done for fungal leaf spot.  See:

https://www.planetnatural.com/pest-problem-solver/plant-disease/bacterial-leaf-spot/

Another thing to consider is rather extensive pruning of the shrubs this fall or very early next spring.  The idea behind this suggestion is to encourage new growth coming up from the roots.  Here is a good site about such pruning:

https://www.gardeningknowhow.com/ornamental/shrubs/spirea/pruning-spirea-shrubs.htm

At this point complete removal of your spirea should not be considered.  If next spring they do not sprout new growth, you may have to consider this possibility. 

If you really want to get to the bottom of things, you could send some plant material to the Plant Disease Clinic at the University of Minnesota.  See the following for complete information as well as procedures for submitting samples:

https://pdc.umn.edu/

Good Luck!!