Small Business Tax Certainty and Growth Act of 2015

Expresses the sense of the Senate that Congress should undertake comprehensive tax reform to make the tax system fairer and simpler and to promote economic growth.

Amends the Internal Revenue Code to: (1) make permanent the increased tax deductions for business start-up expenditures, organizational expenditures, and organization and syndication fees; (2) allow the cash accounting method for businesses whose gross receipts do not exceed $10 million (currently, $5 million); (3) exempt businesses whose gross receipts do not exceed $10 million from the requirement to use inventories; (4) make permanent a $500,000 allowance for expensing business assets, including computer software; (5) extend for one year the additional depreciation allowance for business assets (bonus depreciation); and (6) make permanent the 15-year straight-line depreciation allowance for qualified leasehold improvement, restaurant, and retail improvement property.