My uncle ,who lived in California recently died and left me 15% percent of his estate.
Does the State of California tax his estate ? If there is a tax, will this happen before I receive my check?

CA no longer has an estate tax. There may be federal estate taxes due, but only if his estate is valued above $2M. The executor of the estate is responsible for figuring that out, and if any estate tax is due the executor will pay it out of the estate's assets, as well as any other expenses the estate is responsible for (for example: federal and CA income taxes on income the estate may receive while still in probate, mortgage payments or real estate taxes on property, etc) before making final distributions to the heirs. Once you receive your inheritance there will be no further taxes due on the distribution.

Yes, as ebaines state, if the estate of your uncle is over 2 million, the executor of the estate must file estate tax return, and pay estate taxes.

Any inheritance you receive or the distribution you receive is not taxable. There is no federal tax on inheritances. Also CA does not have any inheritance tax. Read: Your U.S. Tax Return: Tax on Inheritances

Just to add, if you receive your inheritance in cash then there is nothing more to be done. However if you received the inheritance in non cash assets (property, stock, etc), then you will need to determine your cost basis for the asset. Generally it's the value at time of death. That cost basis would be used to determine whether you gained income or incurred a loss when you sell the asset.