yes for week 15! enjoy while u can!!
it's only when bb grows bigger and has substantial weight that will compress ur inferior vena cava then its unsafe (this should be around week 26 onwards really depends how big ur bb grows inside u)
now is ur honeymoon period pls enjoy slpinh at ur back before u cant
Btw, if u r worried, baby will kick u till u stop sleeping at ur back. they r smart to detect too, so no worries