My MacBook Pro (15" Core 2 Duo Late 2006) is painfully slow

Install an SSD — biggest single improvement. Max out RAM to 4 GB (2×2 GB). Do a clean install. Consider reverting to Snow Leopard (10.6.8). Snow Leopard is the sweet spot for that hardware — leaner, faster, and still runs 32-bit Carbon apps. If you don’t need Lion-only features (like iCloud 1.0), reinstalling 10.6.8 may give you the best performance.

Before spending money on a museum piece, see if the hard drive is overly full. That will slow performance dramaticaly. You need about 15% free space for things to run normally. '

If you ill-advisedly installed anti-virus or so-called "cleaning" apps, you have a self-inflicted wound. Those are known performance killers, doing more harm than good.

I've added RAM to too many Macs to count. In only one case, a 2003 PowerMac G4 MDD, did the addition of RAM make a perceptible difference in user experience. However, in your case 4 GB is probably a good idea. OWC still lists RAM for that model

https://eshop.macsales.com/shop/memory/MacBook/Pro/Core2/

and I don't recommend buying Mac RAM elsewhere, particular for older Intel Macs. The were very picky and most "Value RAM" failed.

I also do not believe you need the 6GB option OWC lists, Getting to 6GB requires a special and expensive 4GB RAM module. My Mid 2007 Macbook Pro ran fine on 4GB of OWC.

Remember the an occasional restart clears caches and RAM so , with 2 t0 4GB RAM, I recommend a restart every five days ±.

OWC also has the SSD.

https://eshop.macsales.com/shop/ssd/owc/macbook-pro/2006-2008

Although rated at SATA 3G, it can run no faster than SATA 1.5GB on your Macbook Pro because your SATA bus is the slowest version. Your top transfer speeds on a good day will be about 125MB/sec, still twice as fast as your current 4200 rpm mech hard drive. You'lll notice, but not be blown away.

Note OWC offers a "Kit" option for that SSD. Highley recommended. I used their SSD to upgrade one of my MBPs and the kit removed a lot of trouble from the install.

➡️ I have no affiliation with OWC other than as a 20-year customer.

jagmeees204 wrote:

Install an SSD — biggest single improvement. Max out RAM to 4 GB (2×2 GB). Do a clean install. Consider reverting to Snow Leopard (10.6.8). Snow Leopard is the sweet spot for that hardware — leaner, faster, and still runs 32-bit Carbon apps. If you don’t need Lion-only features (like iCloud 1.0), reinstalling 10.6.8 may give you the best performance.

iCloud now requires at least High Sierra. Maybe Lion once had an advantage over Snow Leopard when it came to accessing a very early version of iCloud, but now iCloud supports neither.

System requirements for iCloud - Apple Support

I would be concerned whether the internal Hard Drive may be worn out or failing. An OS upgrade can push an old drive over the edge. You can check the Hard Drive's health by installing & running the "smartctl" utility from the open source SmartmonTools project which surprising seems to support back to macOS 10.3 according to the documentation. Unfortunately DriveDx no longer supports macOS 10.6 so we are left using the command line.

You can download the "smartmontools" utility v7.5 DMG from here:

https://www.smartmontools.org/wiki/Download#InstalltheOSXDarwinpackage

Once installed, you can use the following command in the Terminal app:

sudo  /usr/local/sbin/smartctl  -a  /dev/disk0

You can use this modified version of the command to save the output to a text file on the Desktop called "HardDrive_Health_Report.txt":

sudo  /usr/local/sbin/smartctl  -a  /dev/disk0  |  tee  -a  ~/Desktop/HardDrive_Health_Report.txt

If you post the complete text report here I will review it for you. Use the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar (you need to select all the text in that file followed by Copy so you can paste it into the "Additional Text" box).

aydin41 wrote:

I heard Lion basically doesn't know what memory allocation is, so would 4GB of RAM and possibly an SSD fix the problems?

That model Mac supports a maximum of 3 GB RAM.

I'm not sure what you mean by the first clause of that sentence, but as you determined Lion will run more like a Dog on that Mac. Go back to Snow Leopard.