Question Audio switching cause "lag spike?"

I want to switch from normal music to looped music at a certain point, The Problem is that it cause a "lag spike" or something, Would like to know why it happens and how to fix it, Thanks

Spoiler: Code

Code (CSharp):

1.     public IEnumerator ChangeMusicToLooped(AudioClip Start_Clip, AudioClip Looped_clip, float time)
2.     {
3.         PlayMusic(Start_Clip);
4.         yield return new WaitForSeconds(time);
5.         PlayMusic(Looped_clip);
6.     }

Code (CSharp):

1. StartCoroutine(audioManager.ChangeMusicToLooped(audioManager.Boss_Start, audioManager.Boss_Looped, 15.7f));