Downsize Breast Implants to 150 Cc for Natural Look and Feel?

When downsizing this dramatically, you may be better off considering removing the implants altogether and replacing wtih fat grafting.

You can certainly decrease the size of your implants to a more natural looking size. You may want to consider an implant closer to 250cc so that you can maintain a diameter large enough to still have some fullness above the nipple. 150cc implants have a very small diameter which may result in a shape less antural than you would think. Evaluation with a surgeon in person would be a better way to determine which size would allow you to match your expectations with your outcome.

Dropping the volume of an implant by 150 cc's may improve the "natural" appearance, but you may need a lift.

If you are a small breasted woman and are very thin then any implant may look fake. If you have some amount of your own breast tissue then a small implant 150-200 cc low profile can give you some upper pole fullness while still looking natural. Silicone implants might also be a consideration to give a more natural appearance. Cleavage after replacement surgery also depends on your frame.

A 150 cc implant is a tiny little thing, not really worth having.  If you like the closeness of your 450's you will completely lose this with 150's.   You can certainly downsize an implant but you are talking about too much downsizing.  At that point you might as well have them out.