Where does “quindze” come from?

quindze (Old Spanish) comes from Latin quindecim, from Latin decem, from Latin -nus, from Proto-Italic -nos, from Proto-Indo-European -nós — Creates verbal adjectives from roots.

Ancestry of “quindze”, step by step

Step	Language	Word	Meaning
1	Latin	quindecim	fifteen; 15
2	Latin	decem	ten; 10
3	Latin	-nus	-an
4	Proto-Italic	-nos	Creates verbal adjectives from verb stems
5	Proto-Indo-European	-nós	Creates verbal adjectives from roots

Every word from Proto-Indo-European -nós →Every word from Latin -nus →Every word from Latin decem →