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
I have heard that is not good and sleeping left side is best. hope below article may be useful to you.