I am not sure about Spain, but in many countries school start with Kindergarten around age 5 or 6.
Anything before that is 'pre-school' or 'day care'.
In many places pre-school are typically useful for parents where both parents work, and need full work day child care. This means day cares and pre-schools are open many hours. (and that School may have an after school care program on site, or there might be a private after school care program close to the school).
Those hours you mention are not unusual to me.
In the US, there seem to be a little more 'school' in pre-school than I am used to from for instance Denmark where I was born.
Our current pre-school has hours from 9-15, but they also have extended care from 7 - 18. The before and after school time are set aside for different activities that are more playtime than school time.
In case for your pre-school, I would say it depends on what the hours are used for. Is it 'traditional' schooling (learning letters, numbers, colors, etc), or does this include 'free play' like playing with dolls or cars, or acticities like play-doh and coloring. Does it include outdoor time?
If it does that, I don't think those hours are long at all, and would not cause me any concern.
My own kids (aged 5 and 3) are in pre-school from 8:30 to 16:30 every day. But a lot of that is play time.