Should I use suspended hyphen in the example below like 10-to 15-year-olds?
The time spend by 10 to 15-year-olds on two activities.
Yes, the hyphen should follow 10. In addition, a space should follow this hyphen, indicating that 10- is attached to year-..., not to to:
...the time spent by 10- to 15-year-olds on two activities
Note that spent, the past participle of spend, is employed as an attributive.