Printing: Lower DPI vs image resizing and Higher DPI

That's not an easy question and not a simple PS question at that, either. The decisive factor is the effective DPI or LPI your printer has and both variants could produce good results, just differently. A rather crude laser printer for instance may not at all benefit from upsizing beforehand, as they typically use a fixed, rather wide raster, but a photo inkjet printer with adaptive raster might. Generally it would be good to inquire beforehand with the print shop therefore. Of course nothing is wrong with having enough "meat" and upsizing stuff under controlled condititions. people do it all the time. It may just not be necessary nor do anything for the actual output quality.

Mylenium

i would say you would be better to resample the image to 300 DPI. Essentially Photoshop will be using its dithering to do so, but instead of a blocky 150 dpi image, you are printing a slightly blured 300DPI image. If it were me, I would increase the size of the image to 300dpi and print...