Poor Performance with multiple UICollectionViewCells in one CollectionVIew

I have a CollectionView with multiple cell types. When scrolling between different cell types performance can get very laggy. I'm not exactly sure how to fix it. Here's my cellForItemAtIndexPath:

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

if cellType == "imageCell" {

            let cell = collectionView.dequeueReusableCellWithReuseIdentifier("iCell", forIndexPath: indexPath) as! ImageCell

            //do things for cell

            return cell

        }else if cellType == "mapCell" {

            let cell = collectionView.dequeueReusableCellWithReuseIdentifier("mCell", forIndexPath: indexPath) as! MapCollectionViewCell

            //do things for cell

            return cell

        }else if cellType == "pCell" {

            let cell = collectionView.dequeueReusableCellWithReuseIdentifier("pCell", forIndexPath: indexPath) as! PCell

            //do things for cell

            return cell

        }else if cellType == "detailCell" {

            let cell = collectionView.dequeueReusableCellWithReuseIdentifier("fCell", forIndexPath: indexPath) as! DetailCell

            //do things for cell

            return cell

        }else{
            return UICollectionViewCell()
        }}