My father payed for life insurance for 15 years now, not knowing that it is haram. After 15 years can he take back the amount he payed to the insurance company, ignoring the interest money? Will it be halal?
Yes, as insurance is considered haram because of the presence of riba/interest in it.
And about interest Allah says in quran:
“Those who eat riba will not stand (on the Day of Resurrection) except like the standing of a person beaten by Shaytan (Satan) leading him to insanity…
O you who believe! Be afraid of Allah and give up what remains (due to you) from riba (from now onwards) if you are (really) believers.
And if you do not do it, then take a notice of war from Allah and His Messenger.”
So, you must leave every penny of interest but taking back YOUR money is absolutely ok. For further reading, read this.